"One simple way of reading Darwin is almost anything is possible and animals can be adapted in any way. There's a counter school of thought which says evolution is moulded by physical restrictions too, and that's the most interesting point here."

I think this article is stressing something about heat loads and temperatures that were too high for mammals to get all the way up to dino size.

25,000,000 years of rapidly increasing size and then "Wham!!!", they hit a wall.

On another note, ever since I found out about it, I've loved the idea of an indricotherium.